app-arch/lz4: Backport memory corruption fix (CVE-2021-3520)

Bug: https://bugs.gentoo.org/791952
Signed-off-by: Michał Górny <mgorny@gentoo.org>

app-arch/lz4/files/lz4-1.9.3-negative-memmove.patch

@@ -0,0 +1,22 @@
+From 8301a21773ef61656225e264f4f06ae14462bca7 Mon Sep 17 00:00:00 2001
+From: Jasper Lievisse Adriaanse <j@jasper.la>
+Date: Fri, 26 Feb 2021 15:21:20 +0100
+Subject: [PATCH] Fix potential memory corruption with negative memmove() size
+
+---
+ lib/lz4.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/lib/lz4.c b/lib/lz4.c
+index 5f524d01d..c2f504ef3 100644
+--- a/lib/lz4.c
++++ b/lib/lz4.c
+@@ -1749,7 +1749,7 @@ LZ4_decompress_generic(
+                  const size_t dictSize         /* note : = 0 if noDict */
+                  )
+ {
+-    if (src == NULL) { return -1; }
++    if ((src == NULL) || (outputSize < 0)) { return -1; }
+ 
+     {   const BYTE* ip = (const BYTE*) src;
+         const BYTE* const iend = ip + srcSize;

app-arch/lz4/lz4-1.9.3-r1.ebuild

@@ -18,6 +18,10 @@ IUSE="static-libs"
 
 CMAKE_USE_DIR=${S}/build/cmake
 
+PATCHES=(
+	"${FILESDIR}"/${P}-negative-memmove.patch
+)
+
 multilib_src_configure() {
 	local mycmakeargs=(
 		-DBUILD_STATIC_LIBS=$(usex static-libs)